Spine and Leaf vs Traditional Hierarchical Architecture

Hierarchical designs consist of three network layers: the core, the distribution, and the access.Spine and Leaf design consist of two layers: the spine[core], and the leaf [access].

Under Spine and Leaf design all leaf switches have connection to all spine switches. [Spines switches are not interconnected] Hierarchical design distributes access switch connections between 2 or more distributed switches. [Core and distributed switches are interconnected]

A spine and leaf design pushes traffic along multiple paths to handle the required bandwidth, while providing enough cross-connections to allow any node to reach any other node — effectively placing multiple traffic streams in parallel. Traditional designs aggregate traffic by stacking multiple traffic streams onto a single link and cross-connecting all the devices within a single device or carrying the streams serially, rather than in parallel.